Preparation method of radiation cooling film based on synergistic reflection of micropores and inorganic particles

Abstract

The present invention discloses a radiation cooling film based on the coordinated reflection of micropores and inorganic particles and a preparation method thereof. The radiation cooling film has a functional layer, the functional layer includes a polymer three-dimensional skeleton and inorganic particles, the polymer three-dimensional skeleton is distributed with inorganic particles, and the polymer three-dimensional skeleton has a microporous structure; the inorganic particles and the microporous structure synergistically reflect the sunlight irradiated on the radiation cooling film. The preparation method is to first blend the polymer material, the pore-forming agent and the inorganic particles according to a preset ratio to form a mixture; then extrude the film to form a functional layer film with the pore-forming agent and the inorganic particles distributed inside; then extract the obtained film, remove the pore-forming agent, and form a radiation cooling film with micropores and inorganic particles distributed inside. The radiation cooling film has a simple structure, a wide range of raw materials, a strong visible light reflectivity and an atmospheric window emissivity, and can achieve large-scale efficient continuous production, with high production efficiency and low production cost.

Description

Technical Field

[0001] The invention relates to the technical field of polymer processing and molding, and in particular to a method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles. Background Art

[0002] Radiative cooling is a new type of cooling method that transfers heat to outer space in the form of infrared radiation. Compared with traditional air conditioning cooling methods, it has the advantage of zero energy consumption. The principle of radiative cooling is that there is a transparent window in the 8-13μm band in the earth's atmosphere, which allows objects on the earth to radiate their own heat back to space through the transparent window in the form of thermal radiation and use the universe as the cold end to achieve the purpose of cooling. Generally speaking, objects heat up during the day due to solar radiation, so being able to achieve daytime radiative cooling will be of great practical significance, which requires the radiative cooling film to have a relatively high reflectivity in the solar spectrum band and a high emissivity in the atmospheric window band.

[0003] There are many ways to achieve high reflectivity in the solar spectrum band and high emissivity in the atmospheric window band. In 2014, Asawath P. Raman used chemical deposition to prepare a multilayer material device that can achieve daytime radiative cooling. The structure consists of multiple layers of oxides and metal materials with specific thicknesses. SiO2 is used to ensure the high emissivity of the device in the atmospheric window because its molecular bonds have extremely strong resonance absorption ability near 9μm; HfO2 is used to improve the reflectivity of the device in the solar spectrum due to its high refractive index; and the several layers of metal materials on the substrate ensure the high reflectivity of the device to sunlight. However, its material layer structure is relatively complex and the production efficiency is very low.

[0004] In order to improve production efficiency, Zhai from the University of Colorado dispersed silica microspheres in the polymer polymethylpentene (TPX) by a double-roll-to-roll method, and prepared a large-scale film that is transparent in the solar spectrum band and has selective high emissivity in the 8-13μm band, but its high reflectivity still needs to be achieved by an additional composite silver layer. Its film structure and production process are still relatively complicated.

[0005] In 2018, Mandal of Columbia University designed a porous polyvinylidene fluoride-co-hexafluoropropylene (P(VDF-HFP)) film and successfully prepared it by phase separation after casting. The high emissivity of this porous polymer material comes from the atomic vibration in P(VDF-HFP), and the high reflectivity comes from the multi-level micropores formed during the phase separation process. This method has a simple preparation process and can achieve high reflectivity without a metal backplane, but P(VDF-HFP) is required to achieve high emissivity, which greatly limits the choice of radiation cooling materials.

[0006] In summary, although daytime radiation cooling film has broad application prospects, there are still problems with large-scale production. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a radiation cooling film based on the coordinated reflection of micropores and inorganic particles. The film has a simple structure, a wide range of raw materials, and has strong visible light reflectivity and atmospheric window emissivity.

[0008] Another object of the present invention is to provide a method for preparing the above-mentioned radiation cooling film based on the coordinated reflection of micropores and inorganic particles, which can realize large-scale, efficient and continuous production of radiation cooling molds, and has high production efficiency and low production cost.

[0009] The technical solution of the present invention is: a radiation cooling film based on the coordinated reflection of micropores and inorganic particles, the radiation cooling film has a functional layer, the functional layer includes a polymer three-dimensional skeleton and inorganic particles, the inorganic particles are distributed in the polymer three-dimensional skeleton, and the polymer three-dimensional skeleton has a microporous structure; the inorganic particles distributed in the polymer three-dimensional skeleton and the microporous structure coordinately reflect the sunlight irradiated on the radiation cooling film. In the radiation cooling film structure, the reflectivity of sunlight and the emissivity of the atmospheric window can be effectively improved under the synergistic reflection effect of the inorganic particles and the microporous structure. The main reasons are as follows: first, the particle size of the inorganic particles partially overlaps with the sunlight band, and the scattering effect is enhanced when the light wave is incident; second, in the sunlight band, there is a large difference between the refractive index of the polymer three-dimensional skeleton itself and the refractive index where the inorganic particles are located. According to the Fresnel formula, the greater the refractive index difference before and after the light wave is incident, the greater the final reflectivity, which also promotes the improvement of the reflectivity of the radiation cooling film; third, by adding the microporous structure, on the one hand, the scattering of the corresponding light wave wavelength can be enhanced. More importantly, after the micro / nano multi-level aperture distribution is formed in the radiation cooling film, the light wave is incident on the radiation cooling film, and multiple reflections will occur, the transmittance is further reduced, and the reflectivity is further improved.

[0010] In the three-dimensional polymer skeleton, the micropores in the microporous structure have a pore size of 0.1 to 20 μm and a micropore porosity of 50 to 90%. Tests have shown that within this pore size and porosity range, the reflectivity of the radiation cooling film can be effectively guaranteed to meet actual use requirements, and the radiation cooling film has a good molding effect.

[0011] The main raw materials of the polymer three-dimensional skeleton are one or more of polyolefin materials, polyester materials or fluoroplastics.

[0012] The above-mentioned polyolefin materials mainly include ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP) and the like.

[0013] The above polyester materials mainly include polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), etc.

[0014] The above-mentioned fluoroplastics mainly include polyvinylidene fluoride and its copolymers (PVDF, PVDF-TrFE, PVDF-HFP), ethylene-tetrafluoroethylene copolymer (ETFE), fluorinated ethylene propylene copolymer (FEP), etc.

[0015] The inorganic particles are one or more of silicon monoxide (SiO), silicon dioxide (SiO2), silicon nitride (Si3N4), zinc oxide (ZnO), barium sulfate (BaSO4), fluoride (CaF2 and MgF2), silicon carbide (SiC), chromium oxide (Cr2O3), and boron nitride (BN).

[0016] In the radiation cooling film, the weight ratio of the inorganic particles is ≤50wt%.

[0017] Furthermore, the radiation cooling film also has a support layer, and the support layer is arranged on one or both sides of the functional layer, and the support layer is a polymer film layer with a microporous structure. In this structure, the arrangement of the support layer can greatly improve the structural stability of the entire radiation cooling film. In practical applications, the support layer can bear a large amount of tensile force, and the occurrence of the fracture behavior of the loaded functional layer is greatly delayed; especially when the support layer is arranged on both sides of the functional layer, the support layers on both sides can more evenly disperse the force of the filler layer.

[0018] The main raw material of the support layer is one or more of polyolefin materials, polyester materials or fluoroplastics

[0019] The above-mentioned polyolefin materials mainly include ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE) or polypropylene (PP) and the like.

[0020] The above polyester materials mainly include polyethylene terephthalate (PET), polycarbonate (PC) or polymethyl methacrylate (PMMA) and the like.

[0021] The above-mentioned fluoroplastics mainly include polyvinylidene fluoride and its copolymers (PVDF, PVDF-TrFE, PVDF-HFP), ethylene-tetrafluoroethylene copolymer (ETFE) or fluorinated ethylene propylene copolymer (FEP) and the like.

[0022] The present invention provides a method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles, comprising the following steps:

[0023] (1) blending a polymer material, a pore-forming agent, and inorganic particles according to a preset ratio to form a mixture;

[0024] (2) extruding the mixture into a film to form a monolayer film having pore-forming agents and inorganic particles distributed therein;

[0025] (3) The obtained single-layer film is extracted to remove the pore-forming agent, thereby forming a radiation cooling film with micropores and inorganic particles distributed inside.

[0026] Furthermore, when the radiation cooling film also has a support layer, the preparation method thereof comprises the following steps:

[0027] (1) blending a polymer material, a pore-forming agent and inorganic particles according to a preset ratio to form a functional layer mixture; blending a polymer material and a pore-forming agent according to a preset ratio to form a support layer mixture;

[0028] (2) co-extruding the functional layer mixture and the support layer mixture to form a multilayer film having both the functional layer and the support layer, wherein the functional layer has pore-forming agents and inorganic particles distributed inside, and the support layer has pore-forming agents distributed inside;

[0029] (3) The obtained multilayer film is extracted to remove the pore-forming agent, thereby forming a radiation cooling film; in the radiation cooling film, microporous structures and inorganic particles are distributed in the functional layer, and microporous structures are distributed in the support layer.

[0030] In the above two preparation methods, in order to further improve the performance of the obtained radiation cooling film, in the step (3), before extracting the obtained single-layer film or multi-layer film, the single-layer film or multi-layer film is first biaxially stretched. Experiments and tests show that the cross section of the biaxially stretched radiation cooling film is flat, the fiber orientation in the cross section is obvious, and although the thickness of the radiation cooling film decreases with the increase of the stretching ratio, the hierarchical structure of the radiation cooling film is still retained, which means that each layer of the cooling radiation film is fully stretched, which can maximize the mechanical properties of the radiation cooling film; at the same time, it can be found through testing that during the biaxial stretching process, although the thickness of the radiation cooling film is reduced, the inorganic particles therein do not agglomerate, but remain evenly dispersed, so its reflectivity and atmospheric window emissivity can also be better guaranteed.

[0031] In the above two preparation methods, ultrasonic extraction is used for extraction, and the extraction liquid used in the ultrasonic extraction tank is one of water, ethanol, n-hexane, acetone or chloroform.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The radiation cooling film based on the synergistic reflection of micropores and inorganic particles of the present invention has a simple structure and a wide range of raw materials. It utilizes the synergistic reflection effect of inorganic particles and microporous structure to have a strong visible light reflectivity and atmospheric window emissivity. The actual cooling test shows that the radiation cooling film has an excellent cooling effect and can reduce the temperature by up to 10.52°C compared with the normal ambient temperature.

[0034] 2. In the radiation cooling film based on the coordinated reflection of micropores and inorganic particles of the present invention, the inorganic particles are embedded and dispersed in the three-dimensional polymer skeleton with a microporous structure. The structure has strong stability and the inorganic particles are not easy to fall off, thereby ensuring the stability of the radiation cooling film in practical applications.

[0035] 3. In the radiation cooling film based on the coordinated reflection of micropores and inorganic particles of the present invention, a functional layer is formed by a three-dimensional polymer skeleton with a microporous structure and inorganic particles, and then a support layer is formed by a three-dimensional polymer skeleton with a microporous structure. The radiation cooling film having the support layer and the functional layer is formed at one time by co-extrusion. The formed radiation cooling film has strong stability, and under the action of the support layer, the functional layer is not easily damaged even under large tensile force.

[0036] 4. The radiation cooling film based on the coordinated reflection of micropores and inorganic particles of the present invention can be prepared by a continuous production method. The polymer three-dimensional skeleton is used as the polymer matrix. The material system has low cost and a wide range of material types. The preparation method is simple, easy to operate, and has high production efficiency, which is suitable for large-scale industrial production. In addition, the radiation cooling film replaces the traditional metal reflective substrate with a porous polymer matrix, which simplifies the preparation process of the membrane and reduces the preparation cost of the membrane. At the same time, due to the strong flexibility of the polymer, its application scenarios are greatly broadened, and it has a broad market space.

[0037] 5. When preparing the radiation cooling film based on the coordinated reflection of micropores and inorganic particles of the present invention, the formed radiation cooling film can also be subjected to biaxial stretching treatment to maximize the mechanical properties of the radiation cooling film. At the same time, the thickness of the film layer can be reduced to form an ultra-thin high-strength radiation cooling film. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic cross-sectional view of the radiation cooling film embodiment 1.

[0039] Figure 2 This is a schematic cross-sectional view of the radiation cooling film embodiment 2.

[0040] In the above figures, the components indicated by the reference numerals are as follows: 1 is a functional layer, 2 is a polymer three-dimensional skeleton, 3 is an inorganic particle, 4 is a microporous structure, and 5 is a supporting layer. DETAILED DESCRIPTION

[0041] The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

[0042] Example 1

[0043] This embodiment provides a radiation cooling film based on cooperative reflection of micropores and inorganic particles and a preparation method thereof.

[0044] like Figure 1 As shown, the radiation cooling film includes a functional layer 1, which includes a polymer three-dimensional skeleton 2 and inorganic particles 3. The inorganic particles are distributed in the polymer three-dimensional skeleton, and the polymer three-dimensional skeleton has a microporous structure 4; the inorganic particles distributed in the polymer three-dimensional skeleton and the microporous structure cooperate to reflect sunlight irradiated on the radiation cooling film. In the radiation cooling film structure, the reflectivity of sunlight and the emissivity of the atmospheric window can be effectively improved under the synergistic reflection effect of the inorganic particles and the microporous structure. The main reasons are as follows: first, the particle size of the inorganic particles partially overlaps with the sunlight band, and the scattering effect is enhanced when the light wave is incident; second, in the sunlight band, there is a large difference between the refractive index of the polymer three-dimensional skeleton itself and the refractive index where the inorganic particles are located. According to the Fresnel formula, the greater the refractive index difference before and after the light wave is incident, the greater the final reflectivity, which also promotes the improvement of the reflectivity of the radiation cooling film; third, by adding the microporous structure, on the one hand, the scattering of the corresponding light wave wavelength can be enhanced. More importantly, after the micro / nano multi-level aperture distribution is formed in the radiation cooling film, the light wave is incident on the radiation cooling film, and multiple reflections will occur, the transmittance is further reduced, and the reflectivity is further improved.

[0045] In the above-mentioned polymer three-dimensional skeleton, the micropore diameter in the microporous structure is 0.1 to 20 μm, and the micropore porosity is 50 to 90%. Experiments have shown that within the range of pore diameter and porosity, the reflectivity of the radiation cooling film can be effectively guaranteed to meet the actual use requirements, and the forming effect of the radiation cooling membrane is good. The main raw materials of the polymer three-dimensional skeleton can be one or more of polyolefin materials, polyester materials or fluoroplastics. Inorganic particles can be one or more of silicon monoxide (SiO), silicon dioxide (SiO2), silicon nitride (Si3N4), zinc oxide (ZnO), barium sulfate (BaSO4), fluoride (CaF2 and MgF2), silicon carbide (SiC), chromium oxide (Cr2O3) or boron nitride (BN).

[0046] In this embodiment, as a preferred solution, the weight ratio of the inorganic particles in the radiation cooling film is ≤50wt%.

[0047] The method for preparing the radiation cooling film based on the coordinated reflection of micropores and inorganic particles mainly comprises the following steps:

[0048] (1) The polymer material, the pore-forming agent and the inorganic particles are blended according to a preset ratio to form a mixture; in this embodiment, the polymer material is UHMWPE, the inorganic particles are SiO2, and the pore-forming agent is liquid paraffin. The specific operation is as follows:

[0049] (1-1) Before blending, UHMWPE and SiO2 are dried in an electric constant temperature drying oven to remove moisture from the materials to avoid problems such as polymer degradation and bubble generation caused by moisture in subsequent melt processing;

[0050] (1-2) Then weigh a certain amount of UHMWPE, liquid paraffin and SiO2, and stir manually to pre-mix the UHMWPE powder and the liquid paraffin;

[0051] (1-3) adding the mixture of the above materials into a pulsating stretching internal mixer, setting the pulsation number to 360 times, and then taking out the material after being homogenized by the stretching flow field, thus forming a mixture to be extruded;

[0052] (2) extruding the mixture into a film to form a monolayer film having pore-forming agents and inorganic particles distributed therein, and water cooling;

[0053] (3) extracting the obtained monolayer film to remove the pore-forming agent, thereby forming a radiation cooling film with micropores and inorganic particles distributed inside; the specific operation process is as follows:

[0054] (3-1) clamping the wet film formed in step (2) on a bracket, immersing it in a beaker filled with n-hexane, placing the beaker in an ultrasonic cleaning machine, and starting the ultrasonic cleaning machine for extraction;

[0055] (3-2) The extracted radiation cooling film is dried in a vacuum oven at a drying temperature of about 40 °C.

[0056] A radiation cooling film with a thickness of about 0.4 mm was prepared by the above method, and was tested and analyzed. The visible light reflectivity was 93.4%, the atmospheric window emissivity was 78.3%, and the tensile strength was 15 MPa.

[0057] Example 2

[0058] This embodiment provides a radiation cooling film based on the coordinated reflection of micropores and inorganic particles and a preparation method thereof. Compared with embodiment 1, the difference is that:

[0059] like Figure 2As shown, the radiation cooling film of this embodiment also has a support layer 5, and the support layers are respectively arranged on both sides of the functional layer, and the support layers are polymer film layers with a microporous structure. In this structure, the provision of the support layer can greatly improve the structural stability of the entire radiation cooling film. In practical applications, the support layer can bear a large amount of tensile force, and the occurrence of the fracture behavior of the loaded functional layer is greatly delayed; especially when the support layers are arranged on both sides of the functional layer, the support layers on both sides can more evenly disperse the force of the filler layer. Among them, the main raw materials of the support layer are one or more of polyolefin materials, polyester materials or fluoroplastics. Since the radiation cooling film of this embodiment has a multi-layer structure, that is, it has a functional layer and a support layer, in order to obtain a radiation cooling film with a more stable structure, co-extrusion is adopted for molding, and its specific preparation method includes the following steps:

[0060] (1) Blending a polymer material, a pore-forming agent and inorganic particles according to a preset ratio to form a functional layer mixture; blending a polymer material and a pore-forming agent according to a preset ratio to form a support layer mixture; the specific blending process is the same as that of Example 1;

[0061] (2) co-extruding the functional layer mixture and the support layer mixture to form a multilayer film having both the functional layer and the support layer, wherein the functional layer has pore-forming agents and inorganic particles distributed inside, and the support layer has pore-forming agents distributed inside;

[0062] (3) The obtained multilayer film is extracted to remove the pore-forming agent to form a radiation cooling film; in the radiation cooling film, microporous structures and inorganic particles are distributed in the functional layer, and microporous structures are distributed in the support layer; the specific extraction process is the same as that in Example 1.

[0063] A radiation cooling film with a thickness of about 0.4 mm was prepared by the above method, and was tested and analyzed. The visible light reflectivity was 95.4%, the atmospheric window emissivity was 79.3%, and the tensile strength was 25 MPa.

[0064] Example 3

[0065] This embodiment is a method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles. Compared with the embodiment 2, the difference is that:

[0066] In order to further improve the performance of the obtained radiation cooling film, in step (3), before extracting the obtained multilayer film, the multilayer film is first biaxially stretched. The specific operation process is as follows: the formed multilayer film is cut into a size of 90×90 mm, the preheating furnace temperature of the biaxial film stretching machine is set to 100° C., the sample residence time is set to 100 s, the stretching rate in both the longitudinal and transverse directions is 80% / s, and after stretching, heat setting is performed for 100 s, and the heat setting temperature is 110° C.

[0067] Through tests and inspections, it is shown that the cross section of the biaxially stretched radiation cooling film is flat, the fiber orientation in the cross section is obvious, and although the thickness of the radiation cooling film decreases with the increase of the stretching ratio, the hierarchical structure of the radiation cooling film is still retained, which means that each layer of the cooling radiation film is fully stretched, which can maximize the mechanical properties of the radiation cooling film; at the same time, it can be found through inspection that during the biaxial stretching process, although the thickness of the radiation cooling film is reduced, the inorganic particles in it do not agglomerate, but remain evenly dispersed, so its reflectivity and atmospheric window emissivity can also be better guaranteed. The thickness of the test sample is about 60 microns, the reflectivity of the radiation cooling film in the solar band is 96.3%, the atmospheric window thermal emissivity is 81.4%, and the tensile strength is 88.6MPa.

[0068] As described above, the present invention can be better implemented. The above embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention; that is, all equivalent changes and modifications made according to the content of the present invention are covered by the scope of protection required by the claims of the present invention.

Claims

1. A method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles, characterized in that: The following steps are involved: (1) Blending a polymer material, a pore-forming agent and inorganic particles in a preset ratio to form a functional layer mixture; blending a polymer material and a pore-forming agent in a preset ratio to form a support layer mixture; (2) co-extruding the functional layer mixture and the support layer mixture to form a multilayer film having both the functional layer and the support layer, wherein the functional layer has pore-forming agents and inorganic particles distributed inside, and the support layer has pore-forming agents distributed inside; (3) firstly biaxially stretching the multilayer film, then extracting the obtained multilayer film to remove the pore-forming agent, thereby forming a radiation cooling film; In the radiation cooling film, microporous structures and inorganic particles are distributed in the functional layer, and microporous structures are distributed in the support layer; The support layer is arranged on one side or both sides of the functional layer; The functional layer includes a polymer three-dimensional skeleton and inorganic particles, and the main raw material of the polymer three-dimensional skeleton is ultra-high molecular weight polyethylene.

2. The method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles according to claim 1, characterized in that: In the three-dimensional polymer skeleton, the micropore diameter in the microporous structure is 0.1-20 μm, and the micropore porosity is 50-90%.

3. The method for preparing a radiation cooling film based on the coordinated reflection of micropores and inorganic particles according to claim 1, characterized in that: The inorganic particles are one or more of silicon dioxide, silicon nitride, zinc oxide, barium sulfate, fluoride, silicon carbide, chromium oxide or boron nitride.

4. The method for preparing a radiation cooling film based on cooperative reflection of micropores and inorganic particles according to claim 1, characterized in that: In the radiation cooling film, the weight ratio of the inorganic particles is ≤50 wt%.

5. The method for preparing a radiation cooling film based on cooperative reflection of micropores and inorganic particles according to claim 1, characterized in that: The main raw materials of the support layer are one or more of polyolefin materials, polyester materials or fluoroplastics.

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